Preliminary evidence in the literature suggests that tumor-specific enzyme changes are present in certain malignant tissues. The possibility of similar changes being present in leukemic cells will be explored in this research proposal by studying the enzyme activities and isoenzyme profiles of hexosaminidase, pyruvate kinase and isocitrate dehydrogenase in the lymphoblasts of children with acute lymphoblastic leukemia. All 3 of the enzymes to be studied have isoenzymic forms which have been found to be coded for on chromosome 15; thus, the pattern of changes found may provide clues to the nature of the leukemic transformation process(es). In addition, serial followup to the patients and comparison with normal resting lymphocytes and normal lymphocytes induced to undergo mitogen-stimulated blast transformation will determine the leukemia-specificity, and therefore, the clinical usefulness as tumor markers, of any differences that may be found.